Reduced complexity precomputation for decision feedback equalizer

Abstract

Techniques for reducing the complexity and power requirements of precompensation units, as well as equalizers, devices, and systems employing such techniques. In an illustrative method for providing high speed equalization, the method comprises: obtaining a channel response that presents trailing intersymbol interference in a signal having a sequence of symbols from a symbol set; determining a distribution of threshold values for a precompensation unit corresponding to said channel response with said symbol set; deriving a reduced set of threshold values from said distribution; and implementing a decision feedback equalizer with a reduced-complexity precompensation unit employing the reduced set of threshold values. In a related illustrative method for providing high speed equalization, the method comprises: obtaining a channel response that presents trailing intersymbol interference in a signal having a sequence of symbols from a symbol set, the channel response and symbol set corresponding to an initial distribution of threshold values for a precompensation unit; deriving a filter that converts the channel response into a modified channel response, the modified channel response and symbol set corresponding to an improved distribution of threshold values in that the improved distribution includes fewer distinct threshold values or reduced spacing between at least some adjacent threshold values; and implementing a decision feedback equalizer with a reduced-complexity precompensation unit employing the threshold values in the improved distribution.

What is claimed is: 
     
       1. A method for providing high speed equalization, the method comprising:
 obtaining a channel response that presents trailing intersymbol interference in a signal having a sequence of symbols from a symbol set; 
 determining a distribution of threshold values for a precompensation unit corresponding to said channel response with said symbol set; 
 deriving a reduced set of threshold values from said distribution; and 
 implementing a decision feedback equalizer with a reduced-complexity precompensation unit employing the reduced set of threshold values. 
 
     
     
       2. The method of  claim 1 , wherein said deriving includes:
 identifying groups of threshold values within said distribution; and 
 combining the threshold values in each group to obtain a replacement threshold value for that group. 
 
     
     
       3. The method of  claim 2 , wherein said replacement threshold value is an average of the threshold values for that group. 
     
     
       4. The method of  claim 2 , wherein said replacement threshold value is a center of a range of the threshold values for that group. 
     
     
       5. The method according to  claim 2 , wherein said identifying groups includes determining a group membership based at least in part on a difference between each threshold value and the replacement threshold value. 
     
     
       6. The method of  claim 5 , wherein a magnitude of said difference is maintained at or below a predetermined limit. 
     
     
       7. The method of  claim 6 , wherein the limit is 10% of a minimum interval between symbols in the symbol set. 
     
     
       8. A method for providing high speed equalization, the method comprising:
 obtaining a channel response that presents trailing intersymbol interference in a signal having a sequence of symbols from a symbol set, the channel response and symbol set corresponding to an initial distribution of threshold values for a precompensation unit; 
 deriving a filter that converts the channel response into a modified channel response, the modified channel response and symbol set corresponding to an improved distribution of threshold values in that the improved distribution includes fewer distinct threshold values or reduced spacing between at least some adjacent threshold values; and 
 implementing a decision feedback equalizer with a reduced-complexity precompensation unit employing the threshold values in the improved distribution. 
 
     
     
       9. The method of  claim 8 , wherein the employing includes deriving a reduced set of threshold values from said improved distribution. 
     
     
       10. The method of  claim 9 , wherein said deriving includes:
 identifying groups of threshold values within said improved distribution; and 
 combining the threshold values in each group to obtain a replacement threshold value for that group. 
 
     
     
       11. The method of  claim 10 , wherein said replacement threshold value is an average of the threshold values for that group. 
     
     
       12. The method of  claim 10 , wherein said replacement threshold value is a center of a range of the threshold values for that group. 
     
     
       13. The method according to  claim 10 , wherein the obtained channel response has an initial spectrum, and wherein said deriving includes providing a modified channel response spectrum that approximates the initial spectrum. 
     
     
       14. The method according to  claim 10 , wherein said identifying groups includes determining a group membership based at least in part on a difference between each threshold value and the replacement threshold value. 
     
     
       15. The method of  claim 14 , wherein a magnitude of said difference is maintained at or below a predetermined limit. 
     
     
       16. The method of  claim 15 , wherein the limit is 10% of a minimum interval between symbols in the symbol set. 
     
     
       17. A channel interface module that comprises a receiver having:
 a front end filter that produces a filtered signal having trailing intersymbol interference in a sequence of symbols from a symbol set, the trailing intersymbol interference and symbol set corresponding to a set of threshold values for a conventional precompensation unit; 
 at least one reduced-complexity precompensation unit that produces at each of multiple time intervals a set of tentative decisions, thereby providing multiple sets of tentative decisions, each tentative decision accounting for a degree of trailing intersymbol interference from a potential sequence of preceding symbol decisions; 
 a selection element that selects from the multiple sets of tentative decisions an actual sequence of symbol decisions based on preceding symbol decisions in the actual sequence of symbol decisions; and 
 a device interface that provides a host node with a received data stream derived from the sequence of symbol decisions. 
 
     
     
       18. The module of  claim 17 , wherein the front end filter shapes a spectrum of the filtered signal to provide, relative to the spectrum of an optimally filtered signal, fewer distinct threshold values or reduced spacing between at least some adjacent threshold values in the set. 
     
     
       19. The module of  claim 17 , wherein the at least one reduced-complexity precompensation unit comprises a single comparator for each threshold value in a reduced set of threshold values, the reduced set having fewer unique threshold values than said set of threshold values for the conventional precompensation unit. 
     
     
       20. The module according to  claim 17 , wherein the set of threshold values for the conventional precompensation unit includes groups of threshold values, and wherein the at least one reduced-complexity precompensation unit employs a single replacement threshold value for the threshold values in each said group. 
     
     
       21. The module of  claim 20 , wherein said replacement threshold value is an average of the threshold values for that group. 
     
     
       22. The module of  claim 20 , wherein said replacement threshold value is a center of a range of the threshold values for that group. 
     
     
       23. The module of  claim 17 , further comprising a sensor that converts a channel signal into a receive signal, wherein the channel signal is an optical signal, and wherein the front end filter produces the filtered signal in response to the receive signal. 
     
     
       24. The module of  claim 17 , further comprising a sensor that converts a channel signal into a receive signal, wherein the channel is an information storage medium, and wherein the front end filter produces the filtered signal in response to the receive signal. 
     
     
       25. The module of  claim 17 , further comprising a sensor that converts a channel signal into a receive signal, wherein the channel signal is an electromagnetic signal conveyed via twisted wire pair, coaxial cable, or backplane transmission lines, and wherein the front end filter produces the filtered signal in response to the receive signal. 
     
     
       26. The module of  claim 17 , further comprising a forward error correction decoder that derives the received data stream from the sequence of symbol decisions.